Nateglinide, known as (−)-N-(trans-4-isopropylcyclohexanecarbonyl)-D-Phenylalanine, has the following structure and characteristics:
                Formula C19H27NO3         Molecular Weight 317.42        Exact Mass 317.199093        Composition C 71.89% H 8.57% N 4.41% O 15.12%        
Nateglinide is marketed as STARLIX, which is prescribed as oral tablets having a dosage of 60 mg and 120 mg for the treatment of type II diabetes. STARLIX may be used as monotherapy or in combination with metaformin'to stimulate the pancreas to secrete insulin. According to the maker of STARLFX, nateglinide is a white powder that is freely soluble in methanol, ethanol, and chloroform, soluble in ether, sparingly soluble in acetonitrile and octanol, and practically insoluble in water.
Nateglinide may be crystallized out of a mixture of water and methanol, and further dried, as disclosed in U.S. Pat. No. 4,816,484. The procedure of the '484 patent results in a hydrate labeled by the present Applicant(s) as Form Z, or in a methanolate labelled by the Applicant(s) as Form E. Drying of the wet sample results in Form B.
The present invention relates to the solid state physical properties of nateglinide. These properties may be influenced by controlling the conditions under which nateglinide is obtained in solid Form. Solid state physical properties include, for example, the flowability of the milled solid. Flowability affects the ease with which the material is handled during processing into a pharmaceutical product. When particles of the powdered compound do not flow past each other easily, a formulation specialist must take that fact into account in developing a tablet or capsule formulation, which may necessitate the use of glidants such as colloidal silicon dioxide, talc, starch or tribasic calcium phosphate.
Another important solid state property of a pharmaceutical compound is its rate of dissolution in aqueous fluid. The rate of dissolution of an active ingredient in a patient's stomach fluid may have therapeutic consequences since it imposes an upper limit on the rate at which an orally-administered active ingredient may reach the patient's bloodstream. The rate of dissolution is also a consideration in formulating syrups, elixirs and other liquid medicaments. The solid state Form of a compound may also affect its behavior on compaction and its storage stability.
These practical physical characteristics are influenced by the conformation and orientation of molecules in the unit cell, which defines a particular polymorphic Form of a substance. The polymorphic Form may give rise to thermal behavior different from that of the amorphous material or another polymorphic Form. Thermal behavior is measured in the laboratory by such techniques as capillary melting point, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) and may be used to distinguish some polymorphic forms from others. A particular polymorphic Form may also give rise to distinct spectroscopic properties that may be detectable by powder X-ray crystallography, solid state C NMR spectrometry and infrared spectrometry.
Nateglinide exists in various crystalline forms. U.S. Pat. Nos. 5,463,116 and 5,488,150 disclose two crystal forms of nateglinide, designated B-type and H-type, and processes for their preparation. These patents are incorporated herein by reference for their disclosure of the forms. Both forms are characterized by melting point, X-Ray Powder Diffraction (“XRPD”) pattern, IR spectrum in KBr and DSC thermogram. According to these patents, B-type has a melting point of 129–130° C. while H-type has a melting point of 136–142° C. The H-type crystals are characterized in these patents by an XRPD pattern with peaks at 8.1, 13.1, 19.6 and 19.9±0.2 degrees 2θ, and a strong reflection between 15 and 17±0.2 degrees 2θ. The B-type crystal is reported to lack these peaks and have a weak reflection between 15 and 17±0.2 degrees 2θ. H-type crystals are reported to have an IR spectrum with characteristic absorptions at about 1714, 1649, 1542 and 1214 cm−1. These absorptions are reported to be missing in the spectrum of B-type crystals.
According to U.S. Pat. No. 5,463,116, B-type crystals are unstable and susceptible to change during grinding as demonstrated by DSC. The DSC thermogram of B-type shows a sharp endotherm at 131.4° C. before grinding while that of H-type shows a sharp endotherm at 140.3° C. After grinding, the DSC thermogram of B-type shows a second endotherm at 138.2° C., suggesting a solid-solid transformation during grinding.
According to U.S. Pat. No. 5,463,116, the temperature during crystallization and filtration determines whether the crystal Form is B-type or H-type. Temperatures above 10° C., more preferably above 15° C., lead to formation of H-type, while those below 10° C. lead to formation of B-type.
Another crystalline form of nateglinide designated Type-S is disclosed in two Chinese articles: ACTA Pharm. Sinica 2001, 36(7), 532–34 and Yaowu Fenxi Zazhi, 2001, 21(5), 342–44. Form S is reported to be distinguisheable from Forms B and H by a melting point of 172.0° C., a Fourier Transform IR with a peak at 3283 cm−1 (as supposed to 3257 cm−1 and 3306 cm−1 for Forms B and H respectively) and an XRPD pattern with a strong peak at 3.78±0.2 degrees 2θ.
U.S. Pat. No. 5,463,116 (“the '116 patent”) lists the methanolate, ethanolate, isopropanolate and acetonitrilate solvates of nateglinide. According to the '116 patent, amorphous nateglinide may be obtained by drying the hydrate and the solvates. The hydrate may be crystallized by dissolving B-type crystals in a 1.5:1 mixture of ethanol and water, followed by crystallization, as disclosed in Example B-3 of the '116 patent.
The present Applicants obtained a hydrate of nateglinide which the Applicants labeled as Form Z. However, repeating of Example B-3 or comparative Example A3 of the '116 patent also results in Form Z, as well as the crystallization procedure of the '484 patent. Form Z is obtained when only water is present, but Form E methanolate or ethanolate when both methanol or ethanol and water are present.
WO 02/34713, a PCT publication in Japanese, provides in its abstract: “A process for preparing B form nateglinide crystals containing substantially no H-form crystals, which comprises the step of drying wet crystals of a nateglinide solvate at a low temperature until the solvent disappears and then causing them to undergo a crystal transition.” According to the Applicant's translation of Example 1 of the WO publication: “Nateglinide H-form crystals (24.5 kg) were added to ethanol (360 L) and stirred to dissolution at room temperature. After dissolution was confirmed (the mixture) was cooled to 5° C. and allowed to mature at 5° C. for one hour. The deposited crystals were separated and damp crystals (43.0 kg) obtained. These were dried at 45° C. in a rack drier for 24 hours (water content ca. 1%) and then heated for 12 hours at 90° C. to bring about a crystal transformation, when dry crystals (13.3 kg) were obtained. When these crystals were measured by DSC, the characteristic B-form peak was detected (mp ca. 130° C.) but the characteristic H-form peak (mp ca. 139° C.) was not detected. Hence the crystals obtained were of the B-form only and the H-form was concluded to be essentially absent.”
According to the Applicants' translation of Page 3, Line 2 of the WO publication: “The moist solvate crystals obtained (BS: from the cooled solution) are dried till the solvent disappears. The temperature for this will differ depending on the type and quantity of solvent, but usually lies below 60° C. and preferably below 50° C. Although there is no lower limit to the temperature, [the drying] is usually carried out at 20° C. or more for economic reasons. Drying is favorably carried out at usual reduced pressure; at industrially attainable reduced pressures the drying will be complete in a short time. Though the drying at low temperature can be continued to virtual disappearance of the solvent it is not necessary to clear it completely. Even if solvent to the extent of 5% by weight is present this is no problem because it will disappear during the crystal transformation. By heating the dried crystals at 60–110° C., preferably 70–100° C., a crystal transformation into the B-form is brought about. Though the crystal transformation is usually favorably carried out in 0.5 to 48 hours, a period of 1–24 hours is most favored.”
Another PCT publication, WO 03/022251 discloses a crystalline form of nateglinide labeled “AL-type”. The crystalline form is characterized as having a melting point of 174–178° C., an XRPD pattern with peaks at 7.5, 15.5, 19.8 and 20.2 degrees 2θ, and an infra red spectrum with absorption bands in the region 1711.5, 1646.5, 1538.7, 1238.8, 1215.1 and 700.5 cm−1. The crystalline form is obtained in the examples from a solution of acetonitrile under a specific temperature range.
Processes for preparation of nateglinide are disclosed in WO/0232854.
The discovery of new polymorphic forms of a pharmaceutically useful compound provides a new opportunity to improve the performance characteristics of a pharmaceutical product. It enlarges the repertoire of materials that a formulation scientist has available for designing, for example, a pharmaceutical dosage form of a drug with a targeted release profile or other desired characteristic. New polymorphic forms of nateglinide have now been discovered.